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Value Parsers
--------------------------------
To choose proper ``value_parser`` for the attribute, ``traits::attribute_type`` metafunction should be used::
template<class Element, class Attribute>
struct attribute_type
{
typedef /*unspecified*/ type;
};
The returned type can be:
* One of type tags. E.g. **width**, as many others attributes has *<length>* type (corresponds to ``tag::type::length``)::
BOOST_MPL_ASSERT(( boost::is_same<
traits::attribute_type<tag::element::rect, tag::attribute::width>::type,
tag::type::length> ));
* Attribute tag. E.g. **viewBox** has its own syntax::
BOOST_MPL_ASSERT(( boost::is_same<
traits::attribute_type<tag::element::svg, tag::attribute::viewBox>::type,
tag::attribute::viewBox> ));
* Pair *<element tag, attribute tag>*. E.g. **type** attribute may get different values in
elements **animateTransform**, **feColorMatrix**, **feTurbulence** etc.::
BOOST_MPL_ASSERT(( boost::is_same<
traits::attribute_type<tag::element::animateTransform, tag::attribute::type>::type,
boost::mpl::pair<tag::element::animateTransform, tag::attribute::type> > ));
Attribute value parsers interface::
template<class ValueType, class Args..>
struct value_parser
{
template<class AttributeTag, class Context, class AttributeValue, class PropertySource>
static bool parse(AttributeTag tag, Context & context, AttributeValue const & attribute_value,
PropertySource source);
};
``AttributeTag tag``
Is passed to context, isn't used by ``value_parser`` itself
``Context & context``
Reference to the context that will :ref:`receive <passing-values>` parsed value.
``AttributeValue const & attribute_value``
Attribute :ref:`string <passing-string>` value
``PropertySource source``
One of two possible types: ``tag::source::attribute`` or ``tag::source::css``, depending on
whether value if from SVG attribute or CSS property.
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